Frequency divider



Oct. 30, 1951 L. Y. LACY 2,573,150

FREQUENCY DIVIDER Filed Feb. 28, 1946 A TTD/PNP Y Patented et. 30, i951 r .UNITED "s-TATES PATENT OFFICE f :FREQENCYDIVIDER Lester Ilacy," Madison, N. J., assignox` to Bell Telephonej Laboratories,1 Incorporated, New

York;A N.^Y;;a" c'ijporationof "New York VAppl'ieatimfFebruary 2s, 1946, serial No. 650,977

employing electron discharge devices for trans-V mitting current pulses andrelates especially to such circuit means capable of transmitting pulses having a Wide `range of frequency, with stability and reliability.

In another aspect, the invention relates to an improved form of frequency dividing circuit of the so-called bucket anddipper type in which charges on'a small condenser are transferred to a large condenser until a certain value of charge is builtv up on they latter which then discharges into a load circuit. The improvements according to the invention relateto means forV equalizing the steps-.by which the charge is built up on the large condenser; they further relate tothe discharging circuit for `the large. condenser. These improvements aim to increase the range kof freduencies over which the circuit satisfactorily operates and also increase the .range of division ram tios and aid in adjusting to different ratios.

The nature and objects of the invention will appear more fully from the following 'detailed description of the illustrative embodiment shown in the drawing, in which:

Fig. l is a schematic circuit incorporating the invention and Fig. v2 shows graphs ofwave-forms explanatory of' functions to -be described in con-` nection with` Fig. l. v Y

The bucket and dipper method. of frequency division can be made clear fromconsidering the part of Fig. lfrom source Ir up to and including the two condensers and S and diodes l and 8v, all of this part `of the circuitbeing known in the art. It is preferable togl'iavev awslquarepulse `in-A put at the gridof tube 3. and if theseare notv directly available they can be obtained from sine' wave source I-byus'i'ng the type of coupling cir cuits shown for the gridsofl pentodev stages 2 and 3 employing capacity-resistance networks and, series gridfl'irnitingl resistors. `In Fig? 2, if the Wave form at A of' Figl is si usoid'al, a wave Vof square fo'rin B can be deriv'dfat the point designated B in Fig. '1. Each 'tinej'the plate vof tube 3 is driven .,positive, Vsortie'fcrreni'j ilov'vs through condenser 5 intoconderlser through diode 8. When the plate f tube '3` becomes less positive, some current flowsv in the opposite direction through condenser 5 into the platecathode circuit of tube 3` in series with diode 'l and through ground to point I2, but this has no eiect on the charge existing on condenser 6 'since diode 8 is non-conducting under these conditions. In this way, successive increments 'of charge are accumulated on condenser' as indicatedby the 3 claims. (orario-27) idealized staircase curve C until a 'critical voltage is reached at which condenser' vdischarges into the load, producing a sharp pulse'D at each discharge. The graphs are drawn in Fig. 2 to represent' a division ratio of ve between the frequency of VVthe pulses in Wave B and the frequency of vthe pulses D.

The purpose oftleltubeY Sis to at least partially equalize 'the steps Aat C by edualizing the amount of charge Atransferred each timeA into condenser 6. Due to the'ris'ng voltage on the ungrounded terminalA of condenser 6 as its charge increases, smaller and smalleramounts 'of charge would be added to condenser 6 asits charge increases unless some lcompensating provision were made. By use of tube 9 whose grid is Yconr'iected to the ungrounded terminal offcondensr 6, it is possible to make the voltage'V at'E increase at the same rateas the voltage across condenser 6. The voltageat E is determined frorna point on cathoderesistor Il of tube 9. As the grid potentialof'tube 9 becomesnire positive, more current iiows through resistor `Il` raising the potential at E and a point onresistor Il can be found ,by trial `at which the potential at E attains the right value 'to give the desired compensation.

VThe operation ofthe tube v9 in equalizing the steps C will now bey explained by "following through the circuit operation in greater detail. Assuming tube 3 to be a Apentode as illustrated, the pointH will vary in Ypotential between the extremes of plus 200 volts and practically zero (ground) in a time function represented by the B wave, assuming the voltage'of battery 4 to be 200 volts. Starting with condenser 6 fully discharged and `tube 3' conducting at stepfsdffwhen tube 3 is cut 'iravoltage'ef'approxnnatiy r200 'volts isapplied at H to theseries" bj'ranii censietingef condenser sfdiede t arid-eendens'er s, charging eondensers and series "adjj'raising the voltage entendais-ere to si; -jTub-e c issn adjusted, as explained, that 'the potentialatpoint Eis'chan'ged from voltage So"to'voltage Sijdur'- ing the above interval; When the potential at H' gees te' zere the'harge'assumeki'piaced on condenser 5 is. completely 'wipedout 'arid a ysznall reverse `charge placed on 'itfrom' E fraisigthe potential at 4.Tte about Si, so that when pontH again gees positive,A the`v potential at jpoinjt q new starts to rise not' `f'rorir'so asbefre butifrom sr.' The result is that when eenderisers 5 and s are charged by th' indreasef'in potent'ainl 7.2.00 volts at 'point l-I, the`voltage"across" cinienser the tinues through the other steps of the wave C. Another way of stating the action is that the quantity of electricity transferred is the same for each step.

As noted, curve C has been drawn with perfectly square corners on the steps and with the steps exactly equal, both of which are idealized. In practice the corners would be rounded although by using series resistance at 30 the sharpness of the corners can be increased. For frequency dividing purposes theA steps need have only a required degree of equality and the use of tube 9 enables an approach to equality to be realized.

In accordance with one improvement feature of this invention a non-ohmic current-dependent resistor It is inserted between resistor II and the cathode of tube 9 to increase the negative grid bias of tube 9 in the low cathode current condition when the charge on condenser 6 is low and to reduce gradually this bias as the current through the tube increases. This prevents charging condenser 6 by a type of false operation due to initial current flow around the series loop including diodes 'I and 8, condenser 6 and resistor I I, which might occur if the potential at E were even slightly more positive than the upper plate of condenser 6. This condition can further beguarded against by use of a small battery 22 poled to apply a negative voltage to E. As the cathode-ground current of tube 9 increases, the resistance of element ID decreases allowing a greater proportion of the potential drop in the external circuit of tube 9 to appear across resistor I I. The element I may, for example, be a piece of the material known to the trade as thyrite. Varistor I0, therefore, acts similarly to a negative bias battery in the grid lead of tube 9. The use of a battery at this point has the disadvantage that it must be in an ungrounded circuit. the total range through which the voltage of the grid of tube 9 is changed is greater using resistor II) than it would be without this resistor, including the case where the negative grid battery is used.

A further feature of the invention comprises the discharging circuit for the condenser 6, including the tubes I3 and I4. This circuit in and of itself is a known type of flip-flop circuit having a wide frequency range of operation. By not depending upon a time constant circuit while in its stable limiting condition, use of this circuit avoids the tendency to give a false indication when the input frequency changes to a new Value.

Considering the discharge circuit, the circuit is atrest and is stable in the condition where tube I4'is conducting and tube I3 is non-conducting. 'Iubev I4 has no plate load resistor so that its cathode is at relatively high positive potential dueto the current flow through resistor I8. The cathode of tube I3 is also positive, its potential being adjustable by the tap I9 on resistor I8. As the voltage builds up on condenser 6 it reaches the critical point at which tube I3 begins to transmit. Due to the large plate load resistor the potential of the plate falls and drives the grid of tube I4 negative, through the coupling condenser I5. The current in resistor I8 now momentarily decreases because of the falling off of current through tube I4 and because of the limiting effect of resistor 20 on the plate current of tube I3. This action builds itself up until plate current is mostly cut oi in tube I4. The potential of both cathodes falls to near ground and condenser B Also hand plate of condenser I5 has been carried to a potential several volts below ground, e. g., to -v volts, by the drop of potential of the plate of tube I3. This sends current through grid leak resistor I6 in a direction to raise the potential of Vthe grid of tube I4 and this tube begins to draw current raising the potential of the cathode of tube I3 relative to its grid and reducing the current flow through that tube. This action is cumulative and results in reestablishing the stable condition.

While the flip-nop circuit itself is old, its use as a discharge circuit for condenser 6 is believed new and has important advantages, the main one of which is the one mentioned above; namely, greater stability against false indication when the input frequency changes. The circuit also has the advantage of simplicity and ease of adjustment to different frequency-dividing ratios.

The ratio of division of frequency can be varied by varying the slider I9 on resistor I 8, since this determines the critical Voltage at which condenser 5 will discharge through the grid of tube I3.

If the input driving wave should go 01T and then after a time come on again the circuit will restart exactly in step and give the proper division of frequency. Even if the input goes olf for a relatively long time, the circuit I3--I4 will not send a false pulse into the load 2| for it will remain in its stable quiescent condition indenitely. For this same reason the circuit will faithfully divide an input frequency of any value within a wide range.

Certain subject-matter of this disclosure is the basis of a divisional application by the pres-- ent inventor, for Electrical Circuit, Serial No. 240,227, led August 3, 1951.

What is claimed is:

1. In a pulsing circuit, a large condenser to be charged in steps, means to transfer increments of charge to said condenser through a small condenser from a source of voltage varying between xed limits, and means to partially equalize the steps of charge in said large condenser comprising a tube having a cathode, grid and anode, a cathode-grid circuit, and a cathode-anode circuit including a source of anode potential, said tube having its cathode-grid circuit connected across said large condenser and its cathode connected to ground through resistance consisting of a linear resistor adjacent the ground terminal and a non-linear currentdependent resistor in series therewith adjacent the cathode, said resistors having a common junction joint between said cathode and ground, and a connection from said junction point through a unidirectionally conducting element to one terminal of said small condenser.

2. In a pulsing circuit, a condenser to be charged in steps, means to transfer'increments of charge to said condenser, said means comprising a second condenser, a source of voltage varying between fixed limits and a unidirectionally conducting device, said source, second condenser, device and first condenser being connected in series circuit in the order named, and means to partially equalize the steps of charge in said rst condenser comprising a discharge device having a cathode, grid and anode, said grid being connected to a point in said series circuit between said unidirectionally conducting device and one terminal of said rst condenser, a pair of resistors connected in series between said cathode and a point common to the other terminal of said rst condenser, one of said resistors being a current-dependent variable resistor located between said cathode and a common junction point with the other resistor, a cathode-anode circuit including said resistors and a source of anode potential, and a connection from said junction point through a second unidirectionally conducting device to a point in the series circuit between said second condenser and said rst unidirectionally conducting device.

3. In a pulsing circuit, a charge storage condenser, a source of charging potential, means for transferring successive increments of charge to said storage condenser comprising a charge transfer condenser, and means to at least partially equalize the successive increments of charge in said storage condenser, said equalizing means comprising a cathode follower discharge device circuit whose input circuit is connected across said storage condenser, whose cathodeanode circuit includes a source of anode potential, and whose cathode load includes a currentdependent variable resistor, and a connection from a point on said cathode load to one terminal of said transfer condenser for adjusting the potential of said terminal to substantially that of one terminal of the storage condenser upon successive increments of charge of said storage condenser.

LESTER Y. LACY;

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,078,792 Fitzgerald Apr. 27, 1937 2,113,011 White Apr. 5, 1938 2,114,016 Dimond Apr. 12, 1938 2,122,464 Golay July 5,- 1938 2,185,363 White Jan. 2, 1940 2,260,933 Cooper Oct. 28, 1941 2,268,872 Hewlett Jan. 6, 1942 2,403,557 Sanders, Jr July 9, 1946 2,411,573 Holst et al NOV. 26, 1946 2,411,648 Brauer et a1. Nov. 26, 1946 2,413,440 Farrington Dec. 31, 1946 2,415,567 Schoenfeld Feb. 11, 1947 2,416,158 Coykendall Feb. 18, 1947 FOREIGN PATENTS Number Country Date 566,200 Great Britain Dec. 19, 1944 

